Structural build-up and breakdown of sodium hydroxide-activated slag paste assessed using oscillatory rheology

Abstract

Concentrated suspensions of inorganic binders are thixotropic fluids with non-Newtonian behaviour. In addition to the physical-chemical interactions responsible for the flocculation of the particles, the rheological behaviour in time is affected by the formation of the reaction products. In this paper, this topic was tackled using oscillatory rheology, namely, by increasingly used measurements at the constant strain amplitude and frequency over time (time sweep test), by the combination of these tests with an inserted rotational step (ORO test), and by almost unexplored oscillation amplitude sweep tests, leading to structural breakdown due to increasing strain amplitude. Common sodium hydroxide-activated slag paste was used for this purpose. The results showed that the recovery of the structure is not significantly altered if the sample is remixed at least after 30 minutes of reaction. In addition, the strain sweep tests suggested that the formation of the first reaction products started after about 15 minutes of reaction and had a decisive impact on the evolution of viscoelastic moduli and the corresponding stresses during this kind of test.